1. Field of the Invention
The present invention relates to a motor control apparatus and a motor control method.
2. Description of Related Art
A motor control apparatus, which controls rotation of an electric motor, is known (see, for example, Japanese Unexamined Patent Publication No. 2006-320164A). In general, in a case of a motor control apparatus (motor controller) of an air conditioning system, as shown in FIG. 15, when a drive command signal S1 for driving an electric motor 72 is received from an air conditioning electronic control unit (ECU) 70, the motor control apparatus drives the motor 72 according to the received drive signal S1. As shown in FIG. 16, the air conditioning ECU 70 includes an output device 74. The output device 74 is a circuit that includes an NPN transistor 76. An emitter terminal of the transistor 76 is grounded, and a collector terminal of the transistor 76 is connected to one end of a command signal line 80 through a resistor 78. A motor controller (a motor control apparatus) 84 of a blower motor apparatus 82 is connected to the other end of the command signal line 80. In this way, as shown in FIG. 16, the air conditioning ECU 70 and the motor controller 84 are electrically interconnected.
Furthermore, a base terminal of the transistor 76 is connected to a signal generating circuit (not shown), which generates the command signal (ECU output) for driving the motor 72 based on a manipulation signal received from a manipulation switch at the air conditioning ECU 70. Thereby, the base terminal of the transistor 76 receives the command signal (ECU output), which is generated at the air conditioning ECU 70 based on the manipulation signal received from the manipulation switch to drive the motor 72. When the low level signal is supplied to the base terminal of the transistor 76, the electrical conduction between the collector terminal and the emitter terminal of the transistor 76 is turned off (placed in a non-conductive state). When the high level signal is supplied to the base terminal of the transistor 76, the electrical conduction between the collector terminal and the emitter terminal of the transistor 76 is turned on (placed in a conductive state).
In the motor controller 84, the other end of the command signal line 80 is connected to a connection terminal 88 through a resistor 86. A pull-up resistor 90 has one end connected to an electric power source (e.g., an electric power source of 5 V) and the other end connected to the connection terminal 88. Furthermore, a non-inverting input terminal of a comparator 3 is connected to the connection terminal 88. A voltage of a first predetermined value (first threshold value), for example, of 2.5V is supplied to the inverting input terminal of the comparator 3 as a comparative reference voltage. An output terminal of the comparator 3 is connected to an input terminal of a rotation control circuit 92. The comparator 3 compares the first threshold value with an S1 electric potential (electric potential at the connection terminal 88). When the S1 electric potential is equal to or larger than the first threshold value, the high level signal is outputted from the output terminal of the comparator 3. In contrast, when the S1 electric potential is smaller than the first threshold value, the low level signal is outputted from the output terminal of the comparator 3.
A duty ratio of the signal, which is outputted from the output terminal of the comparator 3, is computed as a duty ratio of the drive command signal S1 at the rotation control circuit 92, and the computed duty ratio is used to control the rotation of the motor 72.
Under an ideal circumstance where a disturbance, such as external radio wave radiation (e.g., radio wave radiation from a transceiver, which generates the radio wave), does not exist, when the signal (ECU output) 94 shown in FIG. 17A is supplied to the base terminal of the transistor 76, there is provided the S1 electric potential (electric potential at the connection terminal 88) shown in FIG. 17B. In such a case, the first threshold value, which is used to compute the duty ratio for controlling the rotation of the motor 72, is experimentally obtained and is preset based on the S1 electric potential. Thereby, for example, a period, during which the S1 electric potential is equal to or larger than the first threshold value, may be set as an on-period. Also, a period, during which the S1 electric potential is smaller than the first threshold value, may be set as an off-period. In this way, it is possible to compute the duty ratio for driving the motor 72 based on the S1 electric potential (i.e., the drive command signal S1) and the first threshold value. In the exemplary case of FIGS. 16 and 17B, the first threshold value 98 is set to, for example, 2.5 V.
Furthermore, in the presence of the disturbance, such as the external radio wave radiation, when the signal 96 of FIG. 18A (the signal, which is the same as the signal 94) is supplied to the base terminal of the transistor 76, the S1 electric potential may possibly entirely become below the first threshold value 98, as shown in FIG. 18B. This incidence is most likely caused by the following reason. That is, for example, when the external radio wave is applied to at least one of the command signal line 80 and the air conditioning ECU 70, the electric voltage is applied between the base terminal and the emitter terminal of the transistor 76 of the air conditioning ECU 70. Thereby, even when the signal, which is outputted to turn off the transistor 76, is supplied to the base terminal of the transistor 76, the voltage between the base terminal and the emitter terminal of the transistor 76 does not become 0 V, so that the transistor 76 is placed in the state where the transistor 76 is not completely turned off, i.e., is placed in a low on-state. In such a case, even when the first threshold value 98 is used, it is not possible to accurately compute the duty ratio for driving the motor 72 based on the S1 electric potential. Specifically, in this state where the inverting input terminal of the comparator 3 receives the first threshold value 98 while the non-inverting input terminal of the comparator 3 is connected to the connection terminal 88, when the duty ratio is computed based on the S1 electric potential by using the signal outputted from the output terminal of the comparator 3, the computed duty ratio becomes 0%. Therefore, the motor controller 84 controls the motor 72 such that the motor 72 is not rotated. As discussed above, when the disturbance, such as the external radio wave radiation, exists, the appropriate motor control cannot be performed. In order to address the above disadvantage, for example, a harness having a shield structure may be used for the command signal line 80, or a ferrite bead may be added to improve a radio wave resistance. However, these solutions pose a disadvantage of cost increase.
Furthermore, the motor control apparatus recited in Japanese Unexamined Patent Publication No. 2006-320164A has a soft start function to execute soft start of the electric motor. Also, an inspection apparatus is connectable to the motor control apparatus to inspect the maximum output of the motor. In the motor control apparatus, an external signal determining means determines whether a received drive command signal is a normal operation motor drive command signal or a motor inspection drive command signal. The normal operation motor drive command signal is for commanding a normal operation of the motor, and the motor inspection drive command signal is for commanding the motor inspection operation. This determination process will be described more specifically. The external signal determining means computes a pulse interval, a pulse width, a duty ratio and a frequency of the received signal. When the external signal determining means determines that a frequency f1 (1/T2) and a frequency f2 (1/TC) are alternately repeated in the received signal, the external signal determining means determines that the motor inspection command signal is received. The above determination process is executed by a microcomputer in the motor control apparatus recited in Japanese Unexamined Patent Publication No. 2006-320164A.
However, for example, in the above determination process that senses whether the signal has the frequency f1 and the frequency f2, which are alternately repeated, it requires the relatively long time until the time of making the determination of that the motor inspection command signal is received. That is, due to the relatively long time required for making the determination, the inspection time period is disadvantageously lengthened.